[ivankra]

Vitamin B6 accumulates in the blood - it has an exceptionally long half-life on the order of several weeks. It's not an occasional overdose you have to worry about the most, but also chronic accumulation at low doses (even not much above RDA levels, single digit milligrams) and your blood levels - apparently there's a large individual variation in its metabolism (https://doi.org/10.1016/j.phanu.2020.100188)

UK/EU upper safety limits are at 10-12mg per day. US UL of 200mg is way past due for an overhaul.

I personally got sick from a B complex with 40mg pyridoxine after just 4 months. Developed dysautonomia (not a canonical example, but still a kind of neuropathy - damage to autonomic nervous system). Had random tachycardia and high blood pressure flares from various triggers every week, took a while to figure out what was really causing it. Your typical non-neurologist GP wouldn't know anything because "it's water soluble" and the textbooks say neuropathy develops at 200mg+. All symptoms mostly resolved after a month once I threw away everything with pyridoxine. Wouldn't touch it again, always on a lookout for B6 in my multis and supplements now. P5P form is thought to be safer, but also got people sick - look around on facebook B6 groups for more anecdata.

No problem with B12 as far as I know. It's not a neurotoxin unlike B6.